The overall objective of the proposed research is to identify and analyze in sequential fashion, the key pathological changes which occur during oral carcinogenesis. Carcinogen-altered basal cells, chemically induced in hamster buccal pouch epithelium, will be visualized using histological whole-mount preparations suitable for microscopic inspection of the entire basal epithelial layer. The functional property of "resistance to cytotoxicity", (the ability to proliferate in a cytotoxic environment inhibitory for normal cells), established architectural criteria, and "carcinogen-dose-dependency," will serve as tentative markers for the early detection and quantitation of altered basal cells which are likely initiation sites from which oral cancer can evolve. Once developed the rapid quantitative assay for initiation will be used to clarify specific aspects for oral carcinogenesis, including: (1) the role of cell proliferation in the induction of initiated basal cells, (2) the ability of known or suspected carcinogens to induce initiated cells in oral mucosa, (3) the length of persistence of initiated cells, (4) the role of selective proliferation of initiated cells in the ultimate production of cancer, and (5) the response of initiated cells in oral mucosa to suspected promoting agents. Gamma glutamyltranspeptidase (GGT) activity will be monitored biochemically and histochemically, in whole buccal pouch and in individual mucosal lesions respectively, in order to assess the usefulness of this enzyme as a marker for oral neoplasia. Traditional histopathological criteria, GGT histochemical activity, and 3H-Thymidine-autoradiography will be used to characterize the individual DMBA-induced mucosal lesions at successive stages of neoplastic development and to predict their biological behavior. In addition, the presumptive promoting agents, TPA, ethyl alcohol, and topical vitamin A, will be investigated for their ability to encourage the selective proliferation of putative initiation sites and to promote oral cancer development.